Original Research ARTICLE
Muscle Androgen Receptor Content but Not Systemic Hormones is Associated with Resistance Training-Induced Skeletal Muscle Hypertrophy in Healthy, Young Men
- 1Department of Kinesiology, McMaster University, Canada
- 2Department of Mathematics and Statistics, McMaster University, Canada
- 3Graduate School of Human Development and Environment, Kobe University, Japan
- 4Faculty of Sport and Health Science, Ritsumeikan University, Japan
The factors that underpin heterogeneity in muscle hypertrophy following resistance exercise training (RET) remain largely unknown. We examined circulating hormones, intramuscular hormones, and intramuscular hormone-related variables in resistance-trained men before and after 12 wk of RET. Backwards elimination and principal component regression evaluated the statistical significance of proposed circulating anabolic hormones (e.g., testosterone, free testosterone, dehydroepiandrosterone, dihydrotestosterone, insulin-like growth factor-1, free insulin-like growth factor-1, luteinizing hormone, and growth hormone) and RET-induced changes in muscle mass (n=49). Immunoblots and immunoassays were used to evaluate intramuscular free testosterone levels, dihydrotestosterone levels, 5a-reductase expression, and androgen receptor content in the highest- (HIR; n=10) and lowest- (LOR; n=10) responders to the 12 wk of RET. No hormone measured before exercise, after exercise, pre-intervention, or post-intervention was consistently significant or consistently selected in the final model for the change in: type 1 cross sectional area (CSA), type 2 CSA, or fat- and bone-free mass (LBM). Principal component analysis did not result in large dimension reduction and principal component regression was no more effective than unadjusted regression analyses. No hormone measured in the blood or muscle was different between HIR and LOR. The steroidogenic enzyme 5a-reductase increased following RET in the HIR (P<0.01) but not the LOR (P=0.32). Androgen receptor content was unchanged with RET but was higher at all times in HIR. Unlike intramuscular free testosterone, dihydrotestosterone, or 5a-reductase, there was a linear relationship between androgen receptor content and change in LBM (P<0.01), type 1 CSA (P<0.05), and type 2 CSA (P<0.01) both pre- and post-intervention. These results indicate that intramuscular androgen receptor content, but neither circulating nor intramuscular hormones (or the enzymes regulating their intramuscular production), influence skeletal muscle hypertrophy following RET in previously trained men.
Keywords: Resistance exercise, Testosterone, Intramuscular, androgen receptor, Hypertrophy
Received: 21 May 2018;
Accepted: 10 Sep 2018.
Edited by:Hassane ZOUHAL, University of Rennes 2 – Upper Brittany, France
Reviewed by:Keith Baar, University of California, Davis, United States
Paul T. Reidy, University of Utah, United States
Copyright: © 2018 Morton, Sato, Gallaugher, Oikawa, McNicholas, Fujita and Phillips. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Stuart M. Phillips, McMaster University, Department of Kinesiology, Hamilton, Canada, firstname.lastname@example.org